Assessment of the Synergic Effect between Lysinibacillus sphaericus S-Layer Protein and Glyphosate in the Lethality of the Invasive Arboviral Vector Aedes albopictus

SIMPLE SUMMARY: The tiger mosquito is a novel vector for a variety of viral diseases in Colombia. Glyphosate herbicides have been extensively used in the country as a means to battle illicit crops, namely coca. Negative effects of this compound on arthropods have been reported, but no emphasis on dipterans has been evaluated. Different bacilli bacteria, including the Colombian Lysinibacillus sphaericus, have shown mosquitocidal potential through the production of different proteins. The surface layer (S-Layer) protein, present in this bacterial species, is involved in normal processes, such as protection and shape, but it has been reported as having a role in the mosquitocidal action of the species. In this paper, we evaluate the toxicity of glyphosate, its derivates, and the bacterial S-Layer protein on tiger mosquito larvae, as well as the synergic effect these compounds may have. Bacterial-derived formulations may provide an alternative to chemical pest control and be a viable way to remediate environmental contamination consequences of the drug war. ABSTRACT: Glyphosate and glyphosate-based herbicides are among the most used chemicals in plant pest control. Both glyphosate and its main by-product Aminomethylphosphonic Acid (AMPA) are highly environmentally persistent and, through several processes (including surface runoff and bioaccumulation), affect species beyond their intended targets, especially in aquatic ecosystems. Aedes albopictus is a novel invasive arboviral vector in Colombia and has spread to much of the national territory in recent years. Strains of the bacterium Lysinibacillus sphaericus have shown the ability to degrade glyphosate into environmentally inert compounds, in addition to having great larvicidal efficiency in different mosquito species through the production of several proteins, including the surface layer (S-Layer) protein. The S-Layer is a bacterial structure consisting of glycoprotein monomers, and its functions are thought to include bacterial interactions, protection from the outside medium and biological control. The study assessed the entomopathogenic activity of L. sphaericus S-Layer protein on Ae. albopictus larvae, and the effects that glyphosate and its by-products have in this process. To that end, bioassays were performed to compare the larval mortality between different treatments with and without S-Layer, glyphosate, and glyphosate derivates. Comparisons were made through Analysis of variance (ANOVA) and Tukey’s Honestly Significant Difference (HSD) analyses. Significant differences were found in larval mortality in the treatments, and larval mortality was greater when the S-Layer protein was present, though glyphosate field-doses (1.69 g/L) alone had a notable toxicity as well. An apparent synergic effect on the mortality of larval Ae. albopictus when exposed to mixtures containing 1500 ppm of the S-Layer protein, glyphosate, and/or glyphosate derivates was found. Further studies are needed for the in-depth understanding of this mechanism and its consequences on aquatic ecosystems.